The invention pertains to the field of powered communications interfaces via which DC power is provided to operating circuitry.
Powered communications interfaces are utilized in data communications systems to provide operating power to devices over the same wires used to carry data communications signals, in a manner analogous to the traditional telephone system in which DC operating power is provided to subscriber equipment over the twisted-pair telephone wires. Today, there is widespread use of so-called “power over Ethernet” or POE technology, in which DC operating power is provided to digital telephones, video cameras, and other data terminal equipment over unshielded twisted pair (UTP) cables connecting the data equipment with centralized data switches. In POE parlance, a device receiving power in this fashion is termed a “powered device” or PD, while a device that provides power for use by PDs is termed a “power sourcing equipment” or PSE.
Conventionally, a PSE applies full power (48 volts and a class-based maximum current) to the PD via the powered communication interface as long as the PSE has sufficient incremental power available to do so. The PD uses this POE power to operate. In many cases, the 48 V power is supplied to one or more DC-DC converters in the PD which transform the 48 V power into other specific operating voltages as required by the PD operating circuitry, such as ±15 V, +3.3 V, etc. In particular, the 48 V power is used to provide power to communications circuitry within the PD that effects high-speed data communications to/from the PD over the same twisted pairs used to carry the POE power. This circuitry is commonly referred to by the term PHY, referring to its “physical layer” communications functionality according to the well-known hierarchical description of data network communications.
In some systems a single 4-pair UTP cable may carry POE power from two PSEs to a single PD. The two PSEs may be co-located, or one may be an endpoint device (such as a network switch) and the other an intermediate device such as a midspan power injector. Power from one PSE is supplied to one set of two pairs (e.g., pairs numbered 3,6 and 1,2), while power from the other PSE is supplied to another set of two pairs (e.g., pairs numbered 4,5 and 7,8). The PD may use the two sets of power signals to power two separate loads or a single load by using appropriate circuitry, including protection circuitry to prevent a direct PSE-to-PSE connection from being made within the PD.